Field of the Invention
This invention relates to the monitoring of fluent materials such as liquids within a tank in order to determine the liquid volume, level or flow rate to or from the tank.
The prior art is replete with methods and systems for determining the quantity of liquid or liquid like materials in a tank on a continuous, intermittent or occasional basis. Most common amongst such prior art monitoring systems, are apparatus for determining liquid level in a tank utilizing, for example, a surface level float, an echo ranging device through which signals are reflected from the surface of the liquid being monitored and electromechanical sensors. In addition to acoustical types of devices utilized for monitoring liquid quantity within a tank, electrical devices have also been devised such as those based on the measurement of electrical capacitance.
One serious problem associated with prior liquid quantity monitoring systems arises from changes in the orientation of the liquid enclosing tank or its mounting on a moving vehicle subjecting it to acceleration forces. In an attempt to cope with such problems, acoustical devices utilizing the Helmholtz resonator principle have been proposed, as disclosed for example in U.S. Pat. Nos. 2,666,326, 3,075,382 and 3,324,716. Generally, the acoustical devices based on the Helmholtz resonator principle involve a tank configuration in which a main cavity is formed within which a liquid body is retained below an air space in communication with a restricted throat passage through which acoustical exciting energy is transmitted from an acoustical source and through which the resulting vibrations are sensed. The geometry of such a resonator configuration determines a cavity resonance frequency for the exciting acoustical energy at which resonance occurs as detected by a microphone mounted in the throat passage as explained for example in Roberts U.S. Pat. No. 3,324,716 aforementioned.
The use of the Helmholtz resonator principle in accordance with the prior art exemplified by the aforementioned prior U.S. patents, requires a comparison between the sensor outputs of a standard resonator container excited at its known resonance frequency and a container enclosing an unknown quantity of liquid in order to determine the liquid volume. According to the aforementioned Roberts patent, adjustment of the tank volume is effected until the standard Helmholtz resonator dimension is achieved. Such applications of the Helmholtz resonator principle render the prior art liquid volume monitoring systems relatively limited with respect to installation and application and often inaccurate.
It is therefore an important object of the present invention to provide a volume monitoring system for fluent materials utilizing the Helmholtz resonator principle in a unique and improved manner avoiding the drawbacks and limitations associated with the aforementioned prior art arrangements.
Another object of the present invention in accordance with the foregoing object is to provide an acoustic system for determining the quantity of fluent material within containers in an accurate manner without reliance on volume adjusting or standard resonator comparison techniques.
A further object in accordance with the foregoing objects is to provide a monitoring system not effected by motion of the tank enclosing the fluent material being monitored and not limited by any particular tank geometry or tank orientation.